/* $OpenBSD: dh_check.c,v 1.25 2022/07/13 18:38:20 tb Exp $ */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>

#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/err.h>

#include "bn_lcl.h"
#include "dh_local.h"

#define DH_NUMBER_ITERATIONS_FOR_PRIME 64

/*
 * Check that p is odd and 1 < g < p - 1. The _ex version removes the need of
 * inspecting flags and pushes errors on the stack instead.
 */

int
DH_check_params_ex(const DH *dh)
{
        int flags = 0;

        if (!DH_check_params(dh, &flags))
                return 0;

        if ((flags & DH_CHECK_P_NOT_PRIME) != 0)
                DHerror(DH_R_CHECK_P_NOT_PRIME);
        if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0)
                DHerror(DH_R_NOT_SUITABLE_GENERATOR);

        return flags == 0;
}

int
DH_check_params(const DH *dh, int *flags)
{
        BIGNUM *max_g = NULL;
        int ok = 0;

        *flags = 0;

        if (!BN_is_odd(dh->p))
                *flags |= DH_CHECK_P_NOT_PRIME;

        /*
         * Check that 1 < dh->g < p - 1
         */

        if (BN_cmp(dh->g, BN_value_one()) <= 0)
                *flags |= DH_NOT_SUITABLE_GENERATOR;
        /* max_g = p - 1 */
        if ((max_g = BN_dup(dh->p)) == NULL)
                goto err;
        if (!BN_sub_word(max_g, 1))
                goto err;
        /* check that g < max_g */
        if (BN_cmp(dh->g, max_g) >= 0)
                *flags |= DH_NOT_SUITABLE_GENERATOR;

        ok = 1;

 err:
        BN_free(max_g);

        return ok;
}

/*
 * Check that p is a safe prime and that g is a suitable generator.
 * The _ex version puts errors on the stack instead of returning flags.
 */

int
DH_check_ex(const DH *dh)
{
        int flags = 0;

        if (!DH_check(dh, &flags))
                return 0;

        if ((flags & DH_NOT_SUITABLE_GENERATOR) != 0)
                DHerror(DH_R_NOT_SUITABLE_GENERATOR);
        if ((flags & DH_CHECK_Q_NOT_PRIME) != 0)
                DHerror(DH_R_CHECK_Q_NOT_PRIME);
        if ((flags & DH_CHECK_INVALID_Q_VALUE) != 0)
                DHerror(DH_R_CHECK_INVALID_Q_VALUE);
        if ((flags & DH_CHECK_INVALID_J_VALUE) != 0)
                DHerror(DH_R_CHECK_INVALID_J_VALUE);
        if ((flags & DH_UNABLE_TO_CHECK_GENERATOR) != 0)
                DHerror(DH_R_UNABLE_TO_CHECK_GENERATOR);
        if ((flags & DH_CHECK_P_NOT_PRIME) != 0)
                DHerror(DH_R_CHECK_P_NOT_PRIME);
        if ((flags & DH_CHECK_P_NOT_SAFE_PRIME) != 0)
                DHerror(DH_R_CHECK_P_NOT_SAFE_PRIME);

        return flags == 0;
}

int
DH_check(const DH *dh, int *flags)
{
        BN_CTX *ctx = NULL;
        int is_prime;
        int ok = 0;

        *flags = 0;

        if (!DH_check_params(dh, flags))
                goto err;

        ctx = BN_CTX_new();
        if (ctx == NULL)
                goto err;
        BN_CTX_start(ctx);

        if (dh->q != NULL) {
                BIGNUM *quotient, *residue;

                if ((quotient = BN_CTX_get(ctx)) == NULL)
                        goto err;
                if ((residue = BN_CTX_get(ctx)) == NULL)
                        goto err;
                if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) {
                        /* Check g^q == 1 mod p */
                        if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx))
                                goto err;
                        if (!BN_is_one(residue))
                                *flags |= DH_NOT_SUITABLE_GENERATOR;
                }
                is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME,
                    ctx, NULL);
                if (is_prime < 0)
                        goto err;
                if (is_prime == 0)
                        *flags |= DH_CHECK_Q_NOT_PRIME;
                /* Check p == 1 mod q, i.e., q divides p - 1 */
                if (!BN_div_ct(quotient, residue, dh->p, dh->q, ctx))
                        goto err;
                if (!BN_is_one(residue))
                        *flags |= DH_CHECK_INVALID_Q_VALUE;
                if (dh->j != NULL && BN_cmp(dh->j, quotient) != 0)
                        *flags |= DH_CHECK_INVALID_J_VALUE;
        }

        is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME,
            ctx, NULL);
        if (is_prime < 0)
                goto err;
        if (is_prime == 0)
                *flags |= DH_CHECK_P_NOT_PRIME;
        else if (dh->q == NULL) {
                BIGNUM *q;

                if ((q = BN_CTX_get(ctx)) == NULL)
                        goto err;
                if (!BN_rshift1(q, dh->p))
                        goto err;
                is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME,
                    ctx, NULL);
                if (is_prime < 0)
                        goto err;
                if (is_prime == 0)
                        *flags |= DH_CHECK_P_NOT_SAFE_PRIME;
        }

        ok = 1;

 err:
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        return ok;
}

int
DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key)
{
        int flags = 0;

        if (!DH_check_pub_key(dh, pub_key, &flags))
                return 0;

        if ((flags & DH_CHECK_PUBKEY_TOO_SMALL) != 0)
                DHerror(DH_R_CHECK_PUBKEY_TOO_SMALL);
        if ((flags & DH_CHECK_PUBKEY_TOO_LARGE) != 0)
                DHerror(DH_R_CHECK_PUBKEY_TOO_LARGE);
        if ((flags & DH_CHECK_PUBKEY_INVALID) != 0)
                DHerror(DH_R_CHECK_PUBKEY_INVALID);

        return flags == 0;
}

int
DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *flags)
{
        BN_CTX *ctx = NULL;
        BIGNUM *max_pub_key;
        int ok = 0;

        *flags = 0;

        if ((ctx = BN_CTX_new()) == NULL)
                goto err;
        BN_CTX_start(ctx);
        if ((max_pub_key = BN_CTX_get(ctx)) == NULL)
                goto err;

        /*
         * Check that 1 < pub_key < dh->p - 1
         */

        if (BN_cmp(pub_key, BN_value_one()) <= 0)
                *flags |= DH_CHECK_PUBKEY_TOO_SMALL;

        /* max_pub_key = dh->p - 1 */
        if (!BN_sub(max_pub_key, dh->p, BN_value_one()))
                goto err;

        if (BN_cmp(pub_key, max_pub_key) >= 0)
                *flags |= DH_CHECK_PUBKEY_TOO_LARGE;

        /*
         * If dh->q is set, check that pub_key^q == 1 mod p
         */

        if (dh->q != NULL) {
                BIGNUM *residue;

                if ((residue = BN_CTX_get(ctx)) == NULL)
                        goto err;

                if (!BN_mod_exp_ct(residue, pub_key, dh->q, dh->p, ctx))
                        goto err;
                if (!BN_is_one(residue))
                        *flags = DH_CHECK_PUBKEY_INVALID;
        }

        ok = 1;

 err:
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);

        return ok;
}